Mask assembly and organic light emitting diode display manufactured using the same

ABSTRACT

A mask assembly includes a frame forming an opening, and a plurality of unit masks which form a plurality of deposition openings, the longitudinal ends of the unit masks being fixed to the frame. At least two adjacent ones of the plurality of unit masks have deposition recesses formed on both sides facing each other. The width of the deposition recesses along a width direction of the unit masks is equal to or greater than the width of the deposition openings along the width direction of the unit masks.

CLAIM OF PRIORITY

This application makes reference to, incorporates the same herein, andclaims all benefits accruing under 35 U.S.C. §119 from an applicationearlier filed in the Korean Intellectual Property Office on the 30 Nov.2011 and there duly assigned Serial No. 10-2011-0126931.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a mask assembly. More particularly, thepresent invention relates to a mask assembly for thin film deposition,and an organic light emitting diode display manufactured using the same.

2. Description of the Related Art

An organic light emitting diode display has self-luminancecharacteristics, and exhibits high-quality characteristics such as lowpower consumption, high luminance, high response speed, etc. The organiclight emitting diode display has a structure in which an organicemission layer is disposed between a pixel electrode and a commonelectrode, and each subpixel includes a pixel electrode and an organicemission layer.

The organic emission layer is formed by a deposition method using a maskassembly. The mask assembly includes band-shaped unit masks having aplurality of deposition openings in correspondence to the organicemission layer and a frame for supporting the unit masks. The unit masksare fixed to the frame by a tensile force applied to the unit masksalong a lengthwise direction, and hence are prevented from hanging downby self weight. Such a split-type mask assembly is advantageous in themanufacture of a large-sized organic light emitting diode display.

The above information disclosed in this Background section is only forenhancement of an understanding of the background of the invention, andtherefore it may contain information that does not form the prior artthat is already known in this country to a person of ordinary skill inthe art.

SUMMARY OF THE INVENTION

The present invention provides a mask assembly which can increase thedeposition quality of an organic emission layer, and an organic lightemitting diode display manufactured using the same.

An exemplary embodiment of the present invention provides a maskassembly including: a frame forming an opening; and a plurality of unitmasks which form a plurality of deposition openings, both longitudinalends of the unit masks being fixed to the frame. At least two adjacentones of the plurality of unit masks have deposition recesses formed onboth sides facing each other, and the width of the deposition recessesalong the width direction of the unit masks is equal to or greater thanthe width of the deposition openings along the width direction of theunit masks.

Each of the deposition openings may include long sides parallel to thewidth direction of the unit masks and short sides parallel to thelengthwise direction of the unit masks. The distance between thedeposition openings along the width direction of the unit masks may besmaller than the distance between the deposition openings along thelengthwise direction of the unit masks.

The deposition recesses may be positioned in parallel with the pluralityof deposition openings along the width direction of the unit masks. Twodeposition recesses formed in at least two unit masks may have the sameshape and the same size, and may be positioned in parallel with eachother along the width direction of the unit masks.

The deposition openings and the deposition recesses may be surrounded byinclined sidewalls, and the shape of one sidewall of the depositionrecesses along the width direction of the unit masks may be identical tothe shape of the sidewalls of the deposition openings along the widthdirection of the unit masks.

Each of the unit masks may include one surface facing a depositionsurface and the opposite surface thereof, and the size of the depositionopenings and deposition recesses observed on the one surface may begreater than the size of the deposition openings and deposition recessesobserved on the opposite surface.

The width w1 of the deposition recesses along the width direction of theunit masks may satisfy the following condition:

w2<w1≦w2+d1/2

where w2 indicates the width of the deposition openings along the widthdirection of the unit masks, and d1 indicates the distance between thedeposition openings along the width direction of the unit masks.

The plurality of deposition openings and deposition recesses may bepositioned in the area corresponding to the opening of the frame.

The unit masks may be used for the deposition of organic emission layersin correspondence to subpixels of first, second and third colors, may befixed to the frame by the tensile force applied along the lengthwisedirection, and may be disposed such that the tensile direction isorthogonal to the arrangement direction of the subpixels of the samecolor. The plurality of deposition openings and deposition recesses maybe positioned in correspondence to the subpixels of any one of thefirst, second and third colors.

An exemplary embodiment of the present invention provides an organiclight emitting diode display including pixel electrodes, organicemission layers and a common electrode which are positioned on asubstrate, the organic emission layers including: first organic emissionlayers positioned in correspondence to one subpixel; and second organicemission layers positioned across two subpixels.

The organic emission layers may realize any one of a plurality ofdifferent colors. Organic emission layers of the same color may bepositioned in a row along a first direction, and organic emission layersof different colors may be positioned alternately along a seconddirection orthogonal to the first direction. The second organic emissionlayers each may be positioned across two adjacent subpixels along thefirst direction.

The length of the second organic emission layers may be more than twotimes the length of the first organic emission layer. The length L2 ofthe second organic emission layer along the first direction may berepresented by the following equation:

L2=2L1+d3

where L1 indicates the length of the first organic emission layers alongthe first direction, and d3 indicates the distance between the firstorganic emission layers along the first direction.

A thin film layer may be positioned at the center of the second organicemission layers along the second direction.

The mask assembly according to the present exemplary embodiment allowsthe sidewalls of the deposition openings and the sidewalls of thedeposition recesses to have a sufficient inclination. As a result, thedeposition quality of the organic emission layers in the entire organiclight emitting diode display can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention, and many of the attendantadvantages thereof, will be readily apparent as the same becomes betterunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings, in which likereference symbols indicate the same or similar components, wherein:

FIG. 1 is an exploded perspective view of a mask assembly according toan exemplary embodiment of the present invention;

FIG. 2 is a plan view of the mask assembly according to the exemplaryembodiment of the present invention;

FIG. 3 is a top plan view showing two unit masks of the mask assemblyshown in FIG. 1 and subpixels of an organic light emitting diodedisplay;

FIG. 4 is a top plan view of the unit masks shown in FIG. 3;

FIG. 5 is a cross-sectional view of unit masks cut away along line V-Vof FIG. 4;

FIG. 6 is a schematic view showing a deposition process of an organicemission layer using the unit masks of FIG. 5;

FIG. 7 is a partial enlarged view showing the unit masks of acomparative example in which only deposition openings are provided, butno deposition recesses are provided;

FIG. 8 is a cross-sectional view of the unit masks cut away alone lineVIII-VIII of FIG. 7;

FIG. 9 is a top plan view showing the organic emission layer of theorganic light emitting diode display manufactured using the maskassembly of FIG. 1; and

FIG. 10 is a schematic cross-sectional view of the organic lightemitting diode display including the second organic emission layersshown in FIG. 9.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention will be described more fully hereinafter withreference to the accompanying drawings, in which exemplary embodimentsof the invention are shown. As those skilled in the art will realize,the described embodiments may be modified in various different ways, allwithout departing from the spirit or scope of the present invention.

FIG. 1 is an exploded perspective view of a mask assembly according toan exemplary embodiment of the present invention; and FIG. 2 is a planview of the mask assembly according to the exemplary embodiment of thepresent invention.

Referring to FIG. 1 and FIG. 2, the mask assembly 100 of the presentexemplary embodiment includes a frame 10 having an opening portion 15and band-shaped unit masks 20, both ends of which are fixed to the frame10. Each unit mask 20 has a plurality of deposition openings 21, and isfixed to the frame 10 by a tensile force applied to the unit mask 20along the lengthwise direction, and hence is prevented from hanging downby self weight.

The frame 10 includes a pair of first support portions 11 arranged inparallel with each other and a pair of second support portions 12orthogonal to the first support portions 11. The first support portions11 may be longer than the second support portions 12. With both endsbeing fixed to the first support portions 11, the unit masks 20 aredisposed in parallel with the second support portions 12. The frame 10requires sufficient rigidity because the unit masks 20, being in atension state, are fixed to the frame 10.

The unit masks 20 are gathered to form one mask 201 for deposition. Theparts of the unit masks 20, other than both end parts fixed to the frame10, are all positioned on the opening portion 15 of the frame 10.Accordingly, in a deposition process to be described later, the unitmasks 20 are disposed between a substrate and a deposition source, thusenabling the deposition of an organic emission layer using thedeposition openings 21.

The unit masks 20 are formed together with deposition recesses to bedescribed below. In FIG. 1 and FIG. 2, the illustration of thedeposition recesses is omitted for the convenience of description.

FIG. 3 is a top plan view showing two unit masks of the mask assemblyshown in FIG. 1 and subpixels of an organic light emitting diodedisplay; and FIG. 4 is a top plan view of the unit masks shown in FIG.3.

Referring to FIG. 3 and FIG. 4, the organic light emitting diode displayincludes a plurality of pixels, and each pixel includes subpixels 30 ofthree colors. The three colors may include red(R), green(G) and blue(B).Subpixels of the same color are positioned in a row along a firstdirection (x-axis direction of FIG. 3), and subpixels 30 of differentcolors are positioned alternately along a second direction (y-axisdirection of FIG. 3) orthogonal to the first direction.

Typically, the unit masks 20 are positioned such that their tensiledirection (lengthwise direction) is consistent with the arrangementdirection of subpixels of the same color. However, the unit masks 20 maybe disposed in the reverse manner if necessary. In the mask assembly 100of the present exemplary embodiment, the unit masks 20 are positionedsuch that their tensile direction is orthogonal to the arrangementdirection (first direction) of the subpixels 30 of the same color.

In FIG. 3, the tensile direction of the unit masks 20 is the seconddirection (y-axis direction), and the arrangement direction of thesubpixels 30 of the same color is the first direction (x-axisdirection). Each unit mask 20 has deposition openings 21 correspondingto the subpixels 30 of one color among the subpixels 30 of the threecolors.

Each of the deposition openings 21 may be formed in an approximatelyrectangular shape having long sides and short sides. The long sides ofthe deposition openings 21 are consistent with the width direction(x-axis direction) of the unit masks 20, and the short sides thereof areconsistent with the lengthwise direction (y-axis direction) of the unitmasks 20. Also, the distance dl (see FIG. 4) between the depositionopenings 21 along the first direction (x-axis direction) is less thanthe distance d2 (see FIG. 4) between the deposition openings 21 alongthe second direction (y-axis direction).

At least two adjacent ones of the plurality of unit masks 20 havedeposition recesses 22 formed on both sides facing each other. Thedeposition recesses 22 are not fully surrounded by the unit masks 20,but are opened toward the sides of the unit masks 20. A predeterminedgap may exist between two adjacent unit masks 20.

The deposition recesses 22 are positioned in parallel with thedeposition openings 21 along the first direction (x-axis direction).Also, the deposition recesses 22 formed in one unit mask 20 and thedeposition recesses 22 formed in another unit mask 22 have the sameshape and the same size, and are positioned in parallel with each otheralong the first direction (x-axis direction).

The width w1 (see FIG. 4) of the deposition recesses 22 along the widthdirection of the unit masks 20 is equal to or greater than the width w2(see FIG. 4) of the deposition openings 21 along the width direction ofthe unit masks 20. At this point, two adjacent unit masks 20 cannotoverlap with each other. Thus, the width w1 of the deposition recesses22 is set to satisfy the following condition (1):

w2<w1≦w2+d1/2   (1)

where d1 indicates the distance between the deposition openings 21 alongthe width direction of the unit masks 20.

Accordingly, like the deposition openings 21, one deposition recess 22corresponds to one subpixel 30, and is used to deposit an organicemission layer corresponding to this subpixel 30.

As two unit masks 20 have respective deposition recesses 22 formed onboth sides facing each other, it is possible to form one organicemission layer positioned across two subpixels 30 by using these twodeposition recesses 22 as one deposition opening.

That is, the mask assembly 100 is able to form organic emission layersin correspondence to one subpixel 30 by using a plurality of depositionopenings 21, and, at the same time, to form organic emission layerspositioned across two subpixels by using two deposition recesses 22. Astructure of an organic emission layer formed using the mask assembly100 of the present exemplary embodiment will be described later.

FIG. 5 is a cross-sectional view of unit masks cut away along line V-Vof FIG. 4; and FIG. 6 is a schematic view showing a deposition processof an organic emission layer using the unit masks of FIG. 5.

Referring to FIG. 5 and FIG. 6, in the deposition process, the unitmasks 20 are positioned between a deposition source 41 and a substrate43 where the organic emission layer 42 is to be deposited. The unitmasks 20 of this type cause the deposition openings 21 and depositionrecesses 22 observed on the top and bottom surfaces of the unit masks 20to have different sizes from each other by forming sidewalls 23 of thedeposition openings 21 and deposition recesses 22 to be inclined.

Specifically, the sizes of the deposition openings 21 and depositionrecesses 22 observed on the surface (bottom surface in FIGS. 5 and 6)facing the deposition source 41, among the top and bottom surfaces ofthe unit masks 20, are larger than the sizes of the deposition openings21 and deposition recesses 22 observed on the surface (top surface inFIGS. 5 and 6) facing the substrate 43.

Moreover, the shape of one sidewall 23 of the deposition recess isidentical to the shape of the sidewalls 23 of the deposition openings 21with respect to the cross-sectional shape of the unit masks 20 along thefirst direction (x-axis direction). That is, the inclination of thesidewalls 23 of the deposition opening 21 is identical to theinclination of one sidewall 23 of the deposition recesses 22.

The inclined sidewalls 23 of the deposition openings 21 and depositionrecesses 22 are for reducing a shadow effect caused by the organicemission layer 42 deposited with a non-uniform thickness. If thesidewalls 23 of the deposition openings 21 and deposition recesses 22cannot secure a sufficient inclination, most of the material emittedfrom the deposition source 41 is bumped against the sidewalls 23, thusfailing to be uniformly deposited on the substrate 43. Accordingly, itis important for the sidewalls 23 to secure a sufficient inclination.

FIG. 7 is a partial enlarged view showing the unit masks of acomparative example in which only deposition openings are provided, butno deposition recesses are provided; and FIG. 8 is a cross-sectionalview of the unit masks cut away alone line VIII-VIII of FIG. 7.

Referring to FIG. 7 and FIG. 8, the unit masks 205 of the comparativeexample have deposition openings 215 and 215 a, but no depositionrecesses under the same condition (in which the tensile direction of theunit masks is orthogonal to the arrangement direction of subpixels ofthe same color, and the long sides of the deposition openings areconsistent with the width direction of the unit masks) as the unit masks20 of the exemplary embodiment.

As for the unit masks 205 of the comparative example, it is difficult tosecure a sufficient distance between both sides of the unit masks 205and the outermost deposition openings 215 a. As a result, it is notpossible to achieve a sufficient inclination at one side of theoutermost deposition opening 215 facing a side of the unit mask 205.

In FIG. 8, one sidewall 235 of the outermost deposition opening 215 afacing the side of the unit mask 205 forms a near vertical inclination.As such, the unit masks of the comparative example suffer a shadoweffect in the outermost deposition opening 215, thereby degrading thedeposition quality of the organic emission layer 425. In FIG. 8, theregions of the organic emission layer 425 where the shadow effect hasoccurred are indicated in black line.

Referring again to FIGS. 5 and 6, the unit masks 20 of the presentexemplary embodiment can fundamentally prevent the shadow effect thatoccurs in the comparative example by forming the deposition recesses 22instead of the outermost deposition openings 215 a of the comparativeexample. That is, it is possible to form the organic emission layer 42of uniform thickness by using two adjacent deposition openings 22 as onedeposition opening, rather than forming the outermost depositionopenings 215 a.

In this manner, the unit masks 20 of the present exemplary embodimentenable the sidewalls 23 of the deposition openings 21 and depositionrecesses 22 to have a sufficient inclination. As a result, thedeposition quality of the organic emission layer 42 in the entireorganic light emitting diode display can be improved.

FIG. 9 is a top plan view showing an organic emission layer of theorganic light emitting diode display manufactured using the maskassembly of FIG. 1.

Referring to FIG. 3 and FIG. 9, the mask assembly 100 is used for thedeposition of an organic emission layer 42 of any one of the first,second and third colors in the first position, and is moved to thesecond position and then used for the deposition of an organic emissionlayer 42 of another one of the first, second and third colors. Also, themask assembly 100 is moved to the third position, and is then used forthe deposition of an organic emission layer 42 of the remaining one ofthe first, second and third colors. The first color may be red (R), thesecond color may be green (G), and the third color may be blue (B).

In the organic light emitting diode display, organic emission layers 42of the same color are positioned in a row along the first direction(x-axis direction), and organic emission layers 42 of different colorsare positioned alternately along the second direction (y-axisdirection). The organic emission layers 42 include first organicemission layers 421, each positioned in correspondence to one subpixel,and second organic emission layers 422, each positioned across twoadjacent subpixels along the first direction.

The length L2 (see FIG. 9) of the second organic emission layers 422 istwo times greater than the length L2 (see FIG. 9) of the first organicemission layers 421. Specifically, the length L2 of the second organicemission layer 422 may be represented by (2L1+d3), where d3 indicatesthe distance between the first organic emission layers 421. At thispoint, the lengths L1 and L2 and the distance d3 are all with respect tothe first direction (x-axis direction). The width of the first organicemission layer 421 along the second direction (y-axis direction) isequal to the width of the second organic emission layer 422.

Even if the second organic emission layer 422 is positioned across twoadjacent subpixels, a pixel electrode (not shown) and a driving circuitpart (not shown) are provided separately for each subpixel. Thus, thesecond organic emission layer 422 can emit light independently for eachsubpixel.

Meanwhile, a predetermined gap may exist between the two unit masks 20shown in FIG. 3. Thus, the organic emission layer 42 may be depositedthrough this gap. A thin film layer 60 generated by this gap is shown inFIG. 9. The thin film layer 60, which is formed by overlapping theorganic emission layers 42 of the three colors, is positioned at thecenter of the second organic emission layers 422 in parallel with thesecond direction (y-axis direction).

FIG. 10 is a schematic cross-sectional view of the organic lightemitting diode display including the second organic emission layersshown in FIG. 9.

The organic light emitting diode display 200 is connected to a pluralityof signal lines, and includes a plurality of subpixels arranged in anapproximate matrix form. FIG. 10 illustrates two subpixels of theplurality of subpixels. Although each subpixel includes a plurality ofthin film transistors, only one thin film transistor 50 is illustratedherein for convenience.

Referring to FIG. 10, a buffer layer 44 is formed on the substrate 43, asemiconductor layer 45 is positioned on the buffer layer 44, and asemiconductor layer 45 is positioned on the buffer layer 44. Thesemiconductor layer 45 includes a channel region 451, a source region452, and a drain region 453. The source region 452 and the drain region453 may be doped with a p-type impurity or n-type impurity.

A gate insulating film 46 is formed on the buffer layer 44 whilecovering the semiconductor layer 45, and a gate electrode 47 is formedon the gate insulating film 46 in correspondence to the channel region451. Next, an interlayer insulating film 48 is formed on the gateinsulating film 46 while covering the gate electrode 47.

A contact hole exposing the source region 452 and the drain region 453is formed on the interlayer insulating film 48 and the gate insulatingfilm 46. A source electrode 51 connected to the source region 452 viathe contact hole and a drain electrode 52 connected to the drain region453 via the contact hole are formed on the interlayer insulating film48.

A planarization layer 49 is formed on the interlayer insulating film 48while covering the source electrode 51 and the drain electrode 52, and acontact hole exposing the drain electrode 52 is formed on theplanarization film 49. A pixel electrode 53 connected to the drainelectrode 52 is formed on the planarization layer 49, and a pixeldefining film 54 is formed on the planarization film 49 while coveringthe pixel electrode 53. An opening exposing part of the pixel electrode53 is formed in the pixel defining film 54.

An organic emission layer 422 is formed in the opening of the pixeldefining film 54, and a common electrode 55 is formed over the entirepixel defining film 54 while covering the organic emission layer 422.The organic emission layer 422 shown in FIG. 10 is a second organicemission layer positioned across two adjacent subpixels. Either one ofthe pixel electrode 53 and the common electrode 55 functions as anelectron injection electrode, and the other one functions as a holeinjection electrode.

The organic emission layer 422 may be formed of an organic materialemitting light of any one of red, green and blue, or a mixture of anorganic material and an inorganic material. An auxiliary layer forimproving the luminous efficiency of the organic emission layer 422 maybe formed on the top and bottom of the organic emission layer 422. Theauxiliary layer may be at least one of a hole injection layer, a holetransport layer, an electron injection layer, and an electron transportlayer.

Either one of the pixel electrode 53 and the common electrode 55 may beformed of a transparent conductive film, and the other one may be formedof a reflective conductive film. The light emitted from the organicemission layer 422 is reflected by the reflective conductive film,passes through the transparent conductive film, and is emitted outsidethe organic light emitting diode display.

Although the above description has been made with respect to an examplein which the organic emission layer 42 realizes red, green and blue, theemission color of the organic emission layer 42 is not limited thereto.

While this invention has been described in connection with what ispresently considered to be practical exemplary embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

1-17. (canceled)
 18. An organic light emitting diode display, comprisingpixel electrodes, organic emission layers and a common electrode allpositioned on a substrate; the organic emission layers comprising: firstorganic emission layers positioned in correspondence to one subpixel;and second organic emission layers positioned across two subpixels. 19.The organic light emitting diode display of claim 18, wherein theorganic emission layers realize any one of a plurality of differentcolors, and organic emission layers of a same color are positioned in arow along a first direction, and organic emission layers of differentcolors are positioned alternately along a second direction orthogonal tothe first direction.
 20. The organic light emitting diode display ofclaim 19, wherein the second organic emission layers each are positionedacross two adjacent subpixels along the first direction.
 21. The organiclight emitting diode display of claim 20, wherein a length of the secondorganic emission layers is more than two times a length of the firstorganic emission layer.
 22. The organic light emitting diode display ofclaim 21, wherein a length L2 of the second organic emission layer alongthe first direction is represented by the following equation:L2=2L1+d3 where L1 indicates a length of the first organic emissionlayers along the first direction, and d3 indicates a distance betweenthe first organic emission layers along the first direction.
 23. Theorganic light emitting diode display of claim 19, wherein a thin filmlayer is positioned at a center of the second organic emission layersalong the second direction